Blood is a body fluid that circulates through the heart, arteries, veins and capillaries, carrying oxygen and nutrients to tissues and removing carbon dioxide and other waste products. It is composed of plasma, red blood cells, white blood cells, and platelets. This document appears to be an introductory section on blood from a larger work on anatomy and physiology by Alankar Shrivastav, an assistant professor at Pharmacy Academy in Moradabad, Uttar Pradesh, India.